The present invention relates to a solenoid driving apparatus.
A fuel injection valve driven by a solenoid is known. A fuel injection valve of this type has a stator containing a solenoid, and an armature connected to a needle, for example. The armature is designed to be attracted by the stator and energized by a spring to separate from the stator. When the solenoid is not excited, the armature is energized by the spring, and the fuel injection valve is closed. When the solenoid is excited, the armature is attracted by the stator against the spring, and the fuel injection valve is opened. In a fuel injection control of an internal combustion engine, this fuel injection valve is provided for each cylinder of the internal combustion engine, and a driving apparatus drives solenoids of each fuel injection valve based on drive pulse signals corresponding to each fuel injection valve. In a driving apparatus of this type, it is possible to share a circuit with regard to driving solenoids of fuel injection valves of which injection periods do not overlap. By this, it is possible to decrease the number of circuit parts and cost.
However, when circuits are shared, there is a fear that a noise mixed in a drive pulse signal may adversely affect the driving apparatus. That is, when a noise is mixed in a drive pulse signal, while a solenoid of one fuel injection valve is driven, a solenoid of the other fuel injection valve may be driven by the noise mixed in the drive pulse signal. In this condition, since both fuel injection valves use common circuits at the same time, it causes a hindrance to the driving apparatus and its operation. For this reason, prevention of malfunctioning due to the noise mixed in the drive pulse signal is desired.
Also, in a driving apparatus like this, from a viewpoint that the closing time of the fuel injection valve is shortened, it is desired that a residual magnetic flux due to eddy currents of the stator and the armature is degaussed by inversely exciting the solenoid for a prescribed time by impressing a voltage with an inverse polarity compared with a polarity during driving, following the end of a holding period, and thereby the resetting of the armature by the spring is promoted.
However, if the solenoid is inversely excited, there is a fear that a noise mixed in a drive pulse signal may cause a hindrance to the driving apparatus. That is, while the solenoid is inversely excited, a starting period signal which permits an impression of a high voltage to the solenoid may be generated by the noise mixed in the drive pulse signal. Since the high voltage and the inverse voltage are simultaneously impressed to a drive circuit of the solenoid under this condition, it causes a hindrance to the driving apparatus and its operation. For this reason, such an inconvenience should be avoided.